1. Field of the Invention
This invention relates to a semiconductor image sensor improved in crosstalk inhibition.
2. Description of the Prior Art
The materials used in the conventional semiconductor image sensors include, among others, the following: EQU a-Si:H, EQU a-Si.sub.1-x C.sub.x :H, EQU a-Si.sub.1-x Ge.sub.x :H, EQU a-SiF:H, EQU a-Si.sub.1-x N.sub.x :H, EQU a-Ge:H, EQU .mu.c-Si:H, EQU .mu.c-Si.sub.1-x C.sub.x :H, EQU .mu.c-Si.sub.1-x Ge.sub.x :H, EQU .mu.c-SiF:H, EQU .mu.c-Si.sub.1-x N.sub.x :H and EQU L .mu.c-Ge:H
wherein the prefix "a-" means that the material designated thereby is an amorphous semiconductor, the prefix ".mu.c-" mean that the material designated thereby is a microcrystalline semiconductor, and x is a number within the range of 0&lt;x&lt;1.0.
The semiconductor image sensors have heretofore been constituted by combining at least one thin film of the p, i or n conduction type, a metal electrode ("M" for short) and a transparent conductive film electrode ("TCO" for short), for example as follows: EQU M/i/p/TCO EQU M/p/i/TCO EQU M/i/TCO EQU M/n/i/p/TCO EQU M/p/i/n/TCO EQU M/i/i/TCO
FIG. 2 illustrates, in longitudinal section, one of the conventional semiconductor image sensors, which is of the construction M/i/p/TCO.
In this example, a common metal electrode 2 is formed on an insulator substrate 1 and then an i-type semiconductor layer 3 and a p-type semiconductor layer 4 are formed in that order. Furthermore, discrete transparent conductive film electrodes 5 are formed on the layer 4 by etching technique combined with photolithography technique, for instance.
A light flux L, applied to this image sensor from its transparent conductive film electrode (5) side, arrives at the semiconductor layers 4 and 3. Here, since the transparent conductive film has been constituted by discrete electrodes, discrete picture elements are formed in the semiconductor layers 4 and 3 disposed between the common metal electrode 2 and respective discrete electrodes 5 and the i-type semiconductor layer 3 of each picture element functions as an active layer to produce photocarriers. As these carriers are collected by discrete transparent conductive film electrodes 5, a picture signal is obtained. There have been cases in which the metal electrode is constituted by discrete electrodes while the transparent conductive film on the light incident side is made the common electrode.
In the conventional semiconductor image sensor mentioned above, the semiconductor layers 4 and 3 are not mechanically divided as are the discrete transparent conductive film electrodes 5 but since the conductivity of the p-type semiconductor layer 4 is generally maintained at a level not higher than 10.sup.-4 S/cm and the dark conductivity of the i-type semiconductor layer 3 at a level not higher than 10.sup.-9 S/cm, no interference conduction takes place between any two neighboring discrete electrodes 5. Nonetheless, on irradiation, the conductivity of the active i-type semiconductor layer 3 increases to a level beyond 10.sup.-7 S/cm, with the result that some conduction takes place between the adjacent discrete electrodes 5 and, hence, the crosstalk problem was inevitable.
To solve this problem, it has been proposed to mechanically divide the semiconductor layers into picture elements by etching technique combined with photolithography technique. However, this procedure makes the sensor manufacturing process complicated. Another means which is conceivable would comprise decreasing the overall photoconductivity of the active layer. This means, however, would markedly decrease the sensor sensitivity since there is a positive correlationship between photocarrier yield and photoconductivity.
Accordingly, it is an object of the invention to inhibit crosstalk in a semiconductor image sensor of the construction comprising a semiconductor layer containing an active layer capable of producing carriers upon exposure to light and electrodes one of which is light-transmitting and between which said semiconductor layer is sandwiched, without mechanically dividing the semiconductor layer and without reducing the sensor sensitivity.